The objective of this project is to study the nature of the host-bacterial interactions in the spectrum of periodontal health to periodontal disease with the ultimate goal of developing means for rapid identification of potentially pathogenic microorganisms. This project is aimed at providing fundamental lesions and in normal sulci from aged individuals with minimal periodontal disease. The predominant cultivable microbiota from the patients will be characterized by cultural techniques. Subsequent identification of these organisms in clinical material will employ immunologic techniques. The periodontopathic potential of prominant groups of microorganisms will also be assessed in experimental animals. Because host resistance factors influence periodontal health or disease humoral antibody responses to selected microorganisms will be studied. Special attention will be focused on the Gram negative anaerobic rods which are numerically prominant in human dental plaque associated with alveolar bone destruction. Such knowledge will be evaluated towards the development of practical means of prevention and control of periodontal disease.